The present invention relates to hydraulic power supplies, and more particularly to air operated volumetric hydraulic power units ideally suited for powering high production multiple head welding machines and like equipment of the type disclosed in my co-pending application, Ser. No. 228,156, filed Jan. 23, 1981, which is a continuation-in-part of Ser. No. 120,112, filed Feb. 8, 1980, and now abandoned.
Machines using fluid motors (e.g., piston and cylinder assemblies) for clamping, actuating tools or welding guns, etc. are generally either pneumatically or hydraulically powered. If high speed is required air is often preferred because it is cleaner and will give faster action than oil at the same supply pressure; however, safety limits on usable pressures result in cylinder sizes which are too large for many applications. Oil can be used at higher pressures, thereby reducing cylinder sizes, but to get fast action relatively large displacement pumps are required. Hydraulic power units therefore tend to be large and costly, and because they have continuously operating pumps (even during the dwell or rest portion of the load cycle, because they must be able to quickly meet any sudden demand) they consume substantial amounts of power (variable displacement pumps may consume only moderate power, but are even more costly), are a source of continuous noise, and generate considerable heat because all excess is dumped back to the reservoir after being raised to working pressure.
It is therefore a primary object of this invention to provide an improved hydraulic power supply which operates on demancd only, i.e., it supplies oil under pressure only when required by the load, thereby virtually eliminating the consumption of power (and attendant operating cost), noise and heat build-up when the load is in the dwell or rest part of its cycle (often a substantial proportion of the total cycle time).
One limitation of the power unit disclosed in my prior co-pending application referenced above is that it is not adaptable for indexing. Thus the present invention has the object of providing an indexable demand hydraulic power unit, particularly for assembly plant operations where indexing is desired, but where speed of operation or high volume is not as important as indexing. Furthermore, the indexing will be provided without the need for an external signal, i.e., the unit will provide low or high pressure oil as required from the unit without presetting the unit for a time delay or due to a volumetric limitation. Also, the machine cycle can be commenced when the unit is at any point of its supply cycle, without any need to reset the unit.
The present invention offers the above features while also providing an intensifier for two stage operation of any hydraulic motors to be driven, in which the hydraulic motor initially advances toward the workpiece at a high rate of speed but with relatively little force, and upon engagement with the workpiece provides a very high force, but with limited displacement. No limit exists on the oil intensified as long as intensification is desired, unlike prior intensifing means which was limited by volmes in slave cylinders. The present invention provides all of the above features as a reciprocating unit in a steady reciprocating motion providing the above objects as the unit travels in either of its operating directions and without monitoring oil flow, and includes intensification in either operating direction of the unit (particularly advantageous if a working piston needs to be forcibly freed). It is desired to provide all of the above features with a unit having a gang of cylinders all of which are being powered in the same stroke rather than in sequence or separately, as done in the prior art. An optional accumulator is also disclosed to provide uniform oil pressure at the end of the stroke for smooth operation and oil supply at the end of the stroke.
Further objects of the present invention concern the provision of a demand type hydraulic power unit which can use less expensive fluids (95/5 oil) without fear of leakage, which is relatively compact and economical, which can provide desired high speeds without reliance on costly, bulk accumulators, and which can be retrofit to existing machines, including a reset of the working cylinders of the machines at the end of the machine operation.
Additional advantages and features of the present invention will become apparent from the subsequent description and the appended claims, taken in conjunction with the accompanying drawing.